1. Field of the Invention
This invention relates to a thermosentive recording material, and more particularly to a thermosensitive recording material with an improved dynamic coloring sensitivity, utilizing a coloring reaction between (i) a leuco dye which is colorless or assumes a pale color at room temperature and (ii) a color developer capable of inducing color formation in the leuco dye upon application of heat thereto.
2. Discussion of Background
Recently, various information recording materials of a non-environmental-pollution type, capable of nursing resources and economizing energy, have been developed and put to practical use for the purpose of dealing with a great variety of abundant information. In particular, thermosensitive recording materials have been widely employed in various fields, for instance, for use with terminal printers for computers and calculators, recorders for medical measurement instruments, low- and high-speed facsimile apparatus, automatic ticket vending machines and thermal copying apparatus, because of the following advantages thereof:
(1) images can be readily recorded on a thermosensitive recording material by simply applying heat thereto without employing a complicated development process;
(2) a relatively simple and small-sized apparatus is usable for preparing a thermosensitive recording material, and the obtained recording material is easily handled and requires a low maintenance cost; and
(3) in the case where paper, which is not costly as compared with other materials, is used as a support, a thermosensitive recording material with the plain paper-like touch is obtainable.
In general, the thermosensitive recording material is prepared by coating a liquid for forming a thermosensitive coloring layer, containing a coloring component capable of inducing color formation upon application of heat thereto, onto the surface of paper, synthetic paper or a plastic film, and then dried. Images are recorded on the recording material thus prepared by a thermal pen or a thermal head.
The conventional thermosensitive recording materials, as disclosed, for instance, in Japanese Patent Publications 43-4160 and 45-14039, have shortcomings in that their thermal response is not quick and they cannot yield color images with high density when high-speed recording is conducted.
In order to eliminate the above shortcomings, 3-N-methyl-N-cyclohexylamino-6-methyl-7-anilinofluoran and 3-dibutylamino-6-methyl-7-anilinofluoran have been developed as leuco dyes having high thermal sensitivity, as disclosed in Japanese Laid-Open Patent Applications 49-109120 and 59-190891, respectively.
Furthermore, Japanese Laid-Open Patent Applications 59-106456 and 59-116262 disclose that images can be recorded at high speed with high thermal sensitivity when 1,7-bis(4-hydroxyphenylthio)-3,5-dioxaheptane or 1,5-bis(4-hydroxyphenylthio)-3-oxapentane is used as a color developer.
Japanese Laid-Open Patent Applications 59-101392, 61-123584, 61-215087 and 61-242889 disclose that a recording material having high thermal sensitivity can be obtained and high-speed printing can also be achieved when the above described leuco dyes and color developers ar used in combination.
However, the dynamic coloring sensitivity of the above-described thermosensitive recording materials is not sufficiently high for use in practice.